Revamp unavailable session response message

[gsamokovarov]

When a user hit this message, it usually means two things:

1. The underlying server have been restarted.
2. The user runs in multi-process server and the request hit a worker,
   which doesn't store the session in memory.

I'm trying to hit the users here about the second case, since we
received yet another report of this happening and people getting
confused of why the console doesn't work.

[gsamokovarov]

@rafaelfranca, @chancancode if anyone of you guys want to chime in and help me tweak the message if needed, that would be great :)

[chibicode]

@gsamokovarov

The README of better_errors says:

Better Errors works by leaving a lot of context in server process memory. If you're using a web server that runs multiple "workers" it's likely that a second request (as happens when you click on a stack frame) will hit a different worker. That worker won't have the necessary context in memory, and you'll see a Session Expired message.

If this is the case for you, consider turning the number of workers to one (1) in development. Another option would be to use Webrick, Mongrel, Thin, or another single-process server as your rails server, when you are trying to troubleshoot an issue in development.

This was helpful for me. So maybe we can add these to the message:

• Mention Puma (e.g. "like Unicorn or Puma")
• Add "Consider turning the number of workers to one (1) or using a different server in development."

I can make a quick PR if this sounds good.

[gsamokovarov]

@chibicode Sure, go ahead.

[chibicode]

@gsamokovarov done! #153